In modern prosthetics, the continuing advances that are being made in neuronal coupling of corresponding drive mechanisms are placing increasing demands on separate actuation of individual components. In addition to the usual requirements for a prosthesis that is as light as possible and that is reliable and also inexpensive, it is desirable for the functioning of the prosthesis to approximate as closely as possible to that of the part of the body that is to be replaced. The prosthesis should as far as possible permit all the activities that are permitted by the replaced part of the body. This generally requires a multiplicity of drive mechanisms and control devices and a greater number of joints.
In the case of hand prostheses in particular, the filigree structure of the hand and its extraordinary flexibility place great demands on a corresponding prosthesis.
For example, in order to move prosthetic fingers relative to a chassis, the chassis or a forearm prosthesis is provided with drive mechanisms that move the prosthetic finger in the palmar and dorsal directions via tensioning means. The tensioning means thus assume the role of the human tendons.
To permit more precise control of the prosthetic finger movement, where the fingers are so compact in size and dimension that they correspond as closely as possible to the human fingers, DE 198 54 762 A1 proposes that a motor is arranged in the proximal and medial members of the finger and that the motor pivots the respective next member of the prosthetic finger via a gear mechanism. This is controlled by neuronal signals. A motor that pivots the distal member is arranged in the medial member. An extension part, which can be connected to an artificial finger pad, is coupled to a fixed toothed wheel via a toothed gear with coupling toothed wheels. When the motor of the medial member of the finger is switched on, the distal member of the finger moves up or down. Corresponding to the movement of the coupling toothed wheels, the extension part tilts up or down. The gear arrangement of the distal member of the finger compensates the relatively long lever that is formed by the connecting member and the extension part. If an object is gripped and secured with the finger pad, the distal member of the finger remains fixed in the corresponding position by virtue of its wormwheel coupling, even after the motor of the medial member of the finger has been switched off.
This arrangement requires a large number of parts, in particular a large number of motors and gear wheels, such that the construction as a whole is complex.